In all organisms, the coordinated regulation of events such as genesis, differentiation, growth, and homeostatic maintenance is dependent on intercellular and intertissue communication. In most cases, these processes are mediated by protein factors. Many secretory factors (humoral factors) which have been discovered are involved in the immune system and hematopoietic system, for example, and are referred to as cytokines, which include lymphokines, monokines, interferons, colony-stimulating factors, tumor necrosis factors, and the like. Their relation to disease and their potential use as drugs continue to be the subject of considerable research.
Humoral factors such as growth factors or peptide hormones produced by endocrine tissue also play an extremely important role in growth and homeostatic maintenance, and their application as drugs is the subject of considerable research.
For example, “tachykinins” is the generic term for a group of physiologically active peptides included in this category, which consist of about 10 amino acids and share in common the following carboxyl terminal sequence motif:
Phe-Xaa-Gly-Leu-Met-NH2 
(the above sequence is an example in which the carboxyl group of the C terminal methionine is amidated, where Xaa can be any amino acid). Substance P, neurokinin A, and neurokinin B are known mammalian tachykinins, and are widely distributed in the central nervous and peripheral nervous systems. These peptides are generally released by the nerves, and in most cases are known to bind to various receptors (NK-1, NK-2, and NK-3) present in the body, thereby producing various forms of physiological activity depending on their activation. Particularly in terms of their pharmacological activity, it is clear from the literature, including Pernow et al., Pharmacol. Rev., Vol. 35, pp. 85-141 (1983), that proteins with the aforementioned carboxyl terminal structure are shared. Examples of such activity are widely ranging, such as smooth muscle contraction, decreased blood pressure, enhanced exocrine function, and stimulated vasopermeability. The release of such peptides is known to induce respiratory diseases such as respiratory inflammation or bronchial contraction, and the release of histamines from mast cells. Substance P, in particular, is believed to be involved in the neurotransmission of pain, including pain associated with migraines and arthritis. These peptides may also be involved in gastrointestinal disorders and diseases such as inflammatory bowel disease, as well as other diseases. In view of the great number of clinical diseases characterized by tachykinin over-involvement, the development of tachykinin receptor antagonists may be useful in controlling such clinical pathologies, and a number of peptide and non-peptide tachykinin receptor antagonists have been developed thus far (Nippon Rinsho, Vol. 48, No. 5, p. 98-104 (1990), The FASEB Journal, Vol. 4, pp. 1606-1615 (1990), and Current Medical Chemistry, Vol. 6, pp. 1375-1388 (1999)).
These protein and peptide factors, which are essential to organisms, have conventionally been found on the basis of their inherent biological activity. Genes with high homology have then been discovered by means of cloning techniques based on homology for known physiologically active proteins. However, it is highly likely that, in addition to these known gene groups, humoral functional molecules, which have not been identified by conventional techniques and whose existence therefore remains unknown, also play a major physiological role in maintaining the health of higher organisms, especially mammals.
More recent research based on bioinformatics has attempted to make biological, medical, and veterinary use of novel gene products, which have been discovered on the basis of DNA sequence data, through the aid of data processing techniques using computers (Trends in Biotechnology), Vol. 14, pp. 294-298 (1996). With recent achievements in the large-scale screening of cDNA libraries, an enormous number of novel genes or candidates have continued to be discovered through the compilation of EST (expressed sequence tag) data. However, much of this sequence data is fragmentary and incomplete. A currently remaining, major issue is that various existing cDNA-related public databases do not always contain the complete expressed genes for various organisms. It can thus be a daunting matter to search for completely novel and useful gene products in such databases. Meanwhile, structural analysis of all the DNA of a given organism, that is, the genome, has currently been completed for several bacteria and fungi (such as yeasts). Although such research for the human genomes is expected to take several years, the number of human genes is estimated to be around a hundred thousand. The genes coding for many secretory proteins or secretory peptides have actually been isolated already. However, that number cannot be understood to include all the genes of the genome. Despite the intense desire to find novel useful products, the aforementioned data processing techniques alone cannot be considered adequate for the elucidation of such genes; proof must be based on more detailed biological or chemical analysis and experimentation.